1. Field of the Invention PA1 emitting electromagnetic wave pulses from sending and receiving antennas moving vertically in the vicinity of a side face of a refractory sample to an inner portion of a sample through the side face thereof; PA1 receiving electromagnetic waves reflected by the sample via the sending and receiving antennas thereby obtaining a crude picture of reflected wave images; and PA1 evaluating an internal structure of the refractory sample based on the crude picture of reflected wave images.
This invention relates to a method of evaluating the internal quality of fused cast refractories which is performed nondestructively.
2. DISCUSSION OF BACKGROUND
Since fused cast refractories are provided with excellent corrosion resistance against molten glass, fused cast refractories have been employed mainly at portions contacting molten glass of a glass tank furnace. Especially, since fused cast refractories containing a large amount of ZrO.sub.2 and having a long service life are used, the service lives of most glass tank furnaces exceed 10 years. However, while a required quality standard of glass products becomes more strict, the operating conditions of the glass tank furnaces likewise become more controlled. Especially, fused cast refractories called "tank blocks" which are employed in side walls of glass tank furnaces require high quality manufacture and operation.
When fused cast refractories are employed in a glass tank furnace, the refractories are preferably lined in accordance with the positions of internal defects thereon so that their service lives are equalized and the service life of the glass tank furnace is not shortened considerably owing to the internal defects of the fused cast refractories. However, when the fused cast refractories of which internal qualities are not sufficiently known, are employed in a glass tank furnace, there are unavoidable cases wherein molten glass flows out from the side walls of the glass tank furnace which was expected to have a sufficient service life, even if dense fused cast refractories, called voidfree (VF) grade are employed. (The VF grade refractory has few defects since a large upper portion of the fused cast refractory having many defects is cut off.)
It is strictly required from users of the glass tank furnaces to precisely evaluate the internal quality of the fused cast refractories so that the above-mentioned troubles are avoided, so that it is possible to dispense with maintenance crews for performing temporarily repairs, and so that a long service life of the glass tank furnace can be ensured.
Recently, the X-ray inspection method or the supersonic inspection method has been commonly employed as a means to investigate the internal qualities of ceramic products. However, in the X-ray inspection method, for the inspection of large-sized ceramic products containing a substance having a low X-ray transmittance, for instance, a substance containing heavy elements such as ZrO.sub.2, an X-ray inspection device having a strong X-rays is necessary. Furthermore, in the supersonic inspection method, it is necessary to use a transmission medium such as water or grease to sufficiently transmit the supersonic waves from an oscillator and to receive the reflected supersonic waves from inside of the sample to be inspected, and the measurement is not simple to carry out.
Furthermore, the inspection results are often displayed simply as an image, which is not sufficient as an inspection method for precisely evaluating the internal quality including the position of defects or specifying a state thereof. Especially, when the sample is the fused cast refractory, a precise evaluation is difficult since there are defects inside thereof such as blow holes, flocks of small pores and coarse crystals mixed with pores.
A recent device for searching underground objects has been proposed wherein a laying state of iron codes in reinforced concrete can be detected by electromagnetic waves, as in Japanese Unexamined Patent Publication Nos. 54191/1990, 52272/1990, and 126176/1990. According to this technology, it is possible to detect presence of iron codes laid at approximately 20 cm depth in the reinforced concrete.
In this device for detecting underground objects, sending and receiving antennas moving in parallel with a sample surface emit electromagnetic waves, and receive electromagnetic waves reflected by aboundary (or object) in the sample having different electric properties (dielectric constant), and thus the device provides a distance from the sample surface to the object, based on the time from sending to receiving, and displays the position of the object and the state of the presence thereof in correspondence with the moving position of the sending and receiving antennas, as a computer-processed image.
Furthermore, in Japanese Unexamined Patent Publication No. 81679/1992, a technology is proposed wherein a remaining thickness of refractories of a glass tank furnace is measured by employing such a device, and it is suggested that the technology can be used for shipping inspection of the refractories.